The objectives of this research are to purify and to characterize the (Ca2 ion plus Mg 2 ion) ATPase from the human erythrocyte plasma membrane. Purification of this membrane constituent will follow membrane protein isolation procedures. Initial procedures will involve differential solubilization of protein species, protein separation by isoelectric focusing and differential protein incorporation into liposomes. Reconstitution studies will allow the investigator to characterize the membrane related requirements of this enzyme, as well as to determine the parameters involved in Ca2 ion transport across the membrane.